Lake Ecology and Description

LAKE DESCRIPTION
Culver Lake is located southwest of the Kittatinny Mountain. A section of the Appalachian Trail overlooks the lake. Formation of the lake occurred about 14-18,000 years ago when glacial materials blocked the valley drainage, thus creating a natural body of water. It is conceivable that at that time, Lake Owassa and Culver Lake were a single body of water. The interim thousands of years during which there was organic sediment deposition, two individual natural lakes formed separated by eutrophic wetlands of about one mile. The level of water of Lake Owassa is about 20 feet higher than Culver Lake and the outlet of Owassa flows to the Inlet of Culver Lake.

Dams were built to control the level of Culver Lake between 1880’s and 1929. The lake level was varied to supply water to mills between the lake and Branchville. The Electric building in Branchville is where a hydroelectric generator supplied Branchville with power using water from Culver Brook. The final dam, a fixed elevation dam, installed by the Normanoch Association in 1929 raised the lake level about 6 feet causing inundation of land that had once been above the lake elevation. Wetlands to the east and west flooded and formed what is known as Stehr Cove and the causeway swamp.

Culver Lake has a maximum depth of about 55 feet and a mean depth of 27 feet. The surface area is 539 acres. The volume of water is 5,275,500,000 gallons. It has a flush rate (turnover) of 2.47 years and a moderately high watershed to lake area of 7.4: 1. There is about 5.5 miles of shoreline.

During the early 1900’s, seasonal cottages were built along the shoreline. By 1930, nearly all of the shoreline properties had been purchased and developed. The properties were platted at an average lot width was 50 – 75 feet. In 1929, the Normanoch Association was formed from 3 original holding companies and the lake was declared private as a result of a landmark lawsuit in 1957.

The lake water quality degraded in the period from 1960 through 1990 mainly due to anthropological eutrophication (man’s activities and development). One of the primary causes of eutrophication is from septic systems leaching nutrients into the ground water to the lake. The number of year round vs. seasonal homes has remained about 50:50. There are about 230 shoreline homes distributed over a five and half mile shoreline. There are nearly 375 homes within a 100 meter distance of the shoreline. Internal phosphorus loading plus external nitrate and phosphorus loading from these sources resulted in degradation of the water quality and the transition of the lake into a eutrophic state during much of the mid-season.

Since Culver Lake is a deep water lake, after mixing in March, it begins to stratify in early spring and becomes strongly stratified by late June. (Stratification is occurring earlier due to climate change). The water below the thermocline, a barrier to mixing, is segregated from any oxygen input except for some layer aeration system (installed in 1990) and the photosynthesis induced oxygen below the thermocline. The biological oxygen demand normally exceeds oxygen sources so that the deepest volume of water in the lake (hypolimniom) becomes anoxic unless the hypolimniom aerator is operating. The layer aeration system provides enough oxygen to prevent nutrient recirculation into the thermocline and thus protect the upper water (epilimniom) from phosphorus. Part of the oxygen introduced by the layer aeration system is absorbed by non-respiratory conversion of ammonia to Nitrate. It also provides DO to improve the habitat for cold water fish.

Lake Stratification and Mixing There are four phases to the lake’s thermal profile during the course of a year. All phases are created by thermal changes that affect the water density as seasonal weather causes heating and cooling of the water. The lake mixes in early spring after ice melts. It then stratifies in mid spring, and remains stratified into fall as solar heating warm the top layer. In late fall, the lake surface cools and mixes down until there is minimal temperature difference then becomes stratified under ice cover. In March, when the surface ice melts, the lake once again mixes down. To summarize, there are two thermal stratification phases and two mixing phases. These phases occur as solar heating and natural wintertime heat loss cause the water density to vary and result in vertical movement within the water column.

LAKE ECOLOGY
A detailed description of the ecology of the lake is outside the scope of this handbook. A simplified version of ecology is described. Culver Lake has a complex ecosystem similar to other fresh water lakes. The ecosystem includes all aquatic animals and plant life. The plants (macrophytes) in the water consist of a wide variety of submerged aquatic vegetation and algae (suspended phytoplankton). The animals consist of invertebrates to large fish, fowl and amphibians.

Plants (Submerged Aquatic Vegetation, SAV, Macrophytes) Plants are rooted in the bottom sediment and derive nourishment (nutrients) from the organic materials in the sediment. A recent Hydrological report (Princeton Hydro) estimated about 200,000 lbs. of sediments enter the lake yearly. Sediment amendments combined with decaying organic matter contain nutrients and stimulate the growth of SAVs. Root systems of SAVs expire CO2 that creates an acidic area in the anaerobic zone of the root system. This acidic zone can solubilize organic substances through bacterial energy exchange and release nutrients of metals including phosphorus.

Culver Lake experiences nuisance weed problems today that did not exist 50 years ago. The invasive species were not in the lake until weed cutting was introduced. Many SAV spread by rhizomes and seed. Growth is influenced by the amount of nutrient availability, light availability, and water temperature. SAV serve an important function in providing a habitat for fish breeding and refuge. Photosynthesis can happen in plants because they have chlorophyll (green in color) that captures the sun’s energy, uses it to make sugar out of carbon dioxide and produce oxygen. The growing cycle of SAV begins very early –even as light penetrates ice covering. Curly leaf pondweed and filamentous algae become established very early. Milfoil and Naiad begin growing when water temperatures moderate in early May and mature by late June and throughout the remainder of the growing season. Eel grass is a late growing native species that begins in July and matures in September. See pictures below: upper left is Curly Leaf, to the right is Southern Naiad and bottom is Eurasian Milfoil.


Southern Naiad

Eurasian Millfoil

Curly Leaf

SAV that are not native to the lake are called invasive species. They accidentally arrived in Culver Lake by dirty boat or weed cutter 15-20 years ago. The greatest nuisance invasive species are Eurasian Milfoil and Southern Naiad. Milfoil is a concern because it rapidly spreads and can grow to the surface in deep water where there is minimum light and can cause large floating masses that block boating paths and shade more indigenous SAV. Naiad is a bush like invasive SAV that covers the bottom and can grow to heights of 2-3 feet. It makes swimming difficult. It is a nuisance in shallow areas along the shoreline. Water fowl like Naiad and in fall can be seen diving for it along the shoreline.

Algae (called phytoplankton) consist of suspended colonies of minute plants that absorb carbon dioxide in the presence of water, light and nutrients such as phosphorus and nitrate and through photosynthesis produce oxygen. Algae in high density cause green, turbid water and affect the desirability of the lake for recreational use.
There are a myriad of species within our lake but for simplicity sake there are four basic types of algae that are of most concern.

Filamentous, is a mossy, slimy, bright green growth that forms on rocks and bottom surfaces in the winter and early spring. It is present in late spring and even early summer coating other SAV and smothering their growth. Filamentous blanketing of the bottom and shading other SAV was observed to retard the growth of Naiad and other SAV.

Diatom is a silicate algae that can be helpful in competing with cyanobacteria. But in Culver Lake, the Diatoms are only present for a short period in spring when the water is cold. After water temperature increases and water density lowers, diatoms do not remain at the upper water because they are not neutral buoyancy creatures and tend to sink to the bottom. The Direct Mixing Diffuser (CMD is one of our aeration devices) that can be operated in spring to reintroduce them into the water column by upwelling. This can delay the point in time when other undesirable algae expand their growth. Early spring water color is amber in part because of the diatom presence.

Diatom
Dinoflagellate

Green Algae is an important part of the lake food web. It is grazed by zooplankton and it competes with other B-G algae for nutrients. Its photosynthetic production of oxygen supplies needed dissolved oxygen to support a healthy fish population that exist in the surface water where fish must live after stratification


Green Algae

Cyanobacteria is also called blue green algae (B- G) and can dominate most all depths from mid to late summer when surface water temperature is above 20 degree centigrade. Various types of B-G are always present. They are known as Eco strategists due to their ability to adapt to environments where other algae cannot survive. Fossils show that B-G algae has existed for millions of years. Through adaption to harsh environments of high salinity, high and low temperature, low oxygen) B-G algae can position themselves by use of a vascular cell structure to adjust buoyancy to where sufficient light or nutrients exist in the water column for survival. They can out compete other algae in low nutrient environments and some are capable of synthesizing nitrogen from the atmospheric nitrogen. To accomplish this, they must absorb large amounts of solar energy in this process. Lake’s such as Culver with relatively low phosphorus are not a problem to B-G algae because they can carry (store) nutrients in areas where sufficient nutrient levels exist.


Microcycstis

Blue Green Bloom

B-G algae in the summer degrade the recreational water quality because they multiply so fast and have the highest algae population. They become so dense that water clarity is reduced below our 2 meter minimum clarity goal. B-G can produce toxins and cause health problems, (skin and eye irritation as well as neurological issues) particularly those specie such as microcysis with harmful algae blooms (HAB). The most prominent species are Aphanizomenon, Anabaena, and Oscillatoria. Fortunately, tests show that Culver Lake has a low level of Microcystis. In large number, as seen above in the Microcystis Bloom picture, can produce toxins.

Zooplankton The green algae and diatom algae are a food source for zooplankton, small herbivores (plant eaters). Culver Lake has insufficient large bodied zooplankton to control algae population. Algae not only causes poor clarity but colors the water a deep green. A current strategy to control algae population is to manipulate the food web within the lake. This bio manipulation is accomplished through stocking predator fish such as walleye and hybrid bass to reduce the population of alewives, the small minnows or shiners that forage on the zooplankton. Bio manipulation at Culver Lake has been going on for about 25 years. In addition, for the past several years, zooplankton are stocked in early spring by a Princeton Hydro. Recent test results for zooplankton have indicated an increase in the number of zooplankton. Below is a picture of Daphnia, a large bodied zooplankton that is a favorite meal for Alewifes. Zooplankton graze on algae and fish graze on zooplankton.


Cladoceran

Copepod

CHEMISTRY
The biology of the lake responds to chemical changes and chemical changes respond to biological processes. Understanding the basic reactions and responses can aid in diagnostic work and in management of the lake. The fundamental processes of chemistry will involve reactions that promote bacterial and biological metabolism during anaerobic and aerobic respiration, iron cycle, nutrient uptake of phosphorus and nitrogen, and other compounds that are reduced in the sediment.

Oxygen A molecule of water (H2O) consists of two atoms of hydrogen and one atom of oxygen. The oxygen that Lake Management is most concerned is dissolved oxygen or DO. This form of oxygen is dissolved in the water and originates from atmospheric oxygen. D.O. is imparted into the water when water and air mix at the surface. D.O. drives all chemical exchanges in the lake involving aerobic decomposition of dissolved organic carbon (D.O.C.) by respiration when the oxygen is reduced and carbon is oxidized. The result of oxidizing carbon is carbon dioxide (CO2) – a necessary component of plant uptake. Aerobic exchanges cause loss of oxygen. Oxygen is one of the basic elements that all aerobic living organisms from bacteria to zooplankton to fish require to exist. The water can retain significant amount of DO depending on the temperature. A secondary supply of DO comes from plant photosynthesis, the process described above. The greater the exposure to light, the greater DO produced. One objective of layer aeration operation is to utilize photosynthesis generated DO below the thermocline to support fish habitat in cooler water. Sufficient light to support photosynthesis can occur at the compensation depth (1% light), at approximately 2x the Secchi disc depth. If this depth extends below the thermocline depth of 5-6 meters, photosynthetically generated DO becomes available to the layer aerator intake and creates the layer oxygen zone that extends from 6 meter down to about 11 meter depth. This expanded zone is called the metalimnion. It prevents soluble phosphorus from mixing up and entering the surface water.

Anaerobic Respiration The amount of DO in the lake is a function of the rate of biological oxygen demand. Dissolved oxygen after spring mixing is near saturation level. However organic matter in the lake and organic matter from the watershed remove D.O. in the process of bacterial decomposition. The general term respiration applies to oxygen absorption in aerobic conditions and chemical energy exchange in anaerobic conditions.

In Culver Lake, when the lake is stratified during the warm months, the water below the thermocline, called the hypolimniom, is separated from the surface water (epilimniom). The DO is consumed so quickly that by the end of July to mid-August, the bottom of the lake becomes nearly devoid of oxygen. Fish, which require at least 5 milligrams of DO per liter cannot survive and thus move upward to the epilimnion. The only oxygen input to the water below the thermocline comes from the layer aeration and hypo limnetic aeration system as mentioned earlier. When the aeration system was under consideration in 1989, volunteer data showed the DO loss exceeded 1100 Kg per day.

The bottom of the lake contains aerobic bacteria that quickly demand the remaining dissolved oxygen. When oxygen and nitrates are gone, many sediment bacteria (Chemotrophes) are capable of using iron or manganese to accept the electrons generated by their metabolism. This process continues the anaerobic reduction of inorganic compounds. They do this by what is called alternate terminal electron acceptance from other compounds. This means that these organisms, working in an anaerobic environment, are capable of reducing (in an electron exchange process) inorganic ferric iron, manganese, and sulfur in that order as they oxidize themselves in the energy exchange. There is a sequence to the anaerobic respiration; first Nitrates, Manganese, Iron and then Sulfur. When respiration reduces iron, the result is the liberation of ferrous iron and the release of phosphate compounds from the sediment into the water. This process causes the “internal generation” of phosphates or “internal loading of phosphorus”. Lake Management monitoring requires sampling at 8 and 12 meter depths during summer stratification in order to measure components of ATEA such as Ammonia, Nitrate, Manganese and Iron as well as Total Phosphorus in order to assess the degree of respiration taking place in the hypolimniom. These sample results monitor the condition (aerobic vs. anaerobic) of the bottom depths and are useful in managing the hypo limnetic aeration system.

Iron Cycle and Phosphorus
Culver Lake is a moderately soft water lake. The lake is also defined as a phosphorus limited lake. This means that the degree of eutrophication (productivity of biota) depends on the amount of available phosphorus for growth. Stratified lakes that are moderately soft and have high iron content are usually less productive and have better clarity because of the iron’s capacity to bind phosphorus and precipitate it to the bottom. The iron-phosphate compounds in the sediment at the bottom will not solubilize and release phosphorus provided the environment does not become strongly anaerobic. Thus, the phosphorus bound to the iron is unavailable to stimulate plant growth. As explained above, if the bottom of the lake becomes anaerobic, regardless of iron availability, phosphorus can be released as described above. This explains why the aeration system is so important in lake management. The aeration system needs to provide sufficient oxygen to prevent the reduction of iron. The hypo limnetic aerator provides sufficient oxygen to prevent phosphate release, assuming the hypolimnium is a small volume of water and the layer units are functioning. If the layer aeration system is not operating successfully, the hypolimniom is very large and the DO is quickly consumed and the environment changes to anaerobic. To summarize, the two ingredients needed to control internal phosphorus recirculation is oxygen and iron. In the 1990’s, iron was added to the lake. Prior to its addition, the total phosphorus (TP) was in the 25-35 ug/l range. By 2002, after the iron cycle reestablished itself, the TP was 5-15 ug/l. Consequently, the mean depth clarity increased from 1.1 to 2.0 meters. This was the result of the iron controlling the internal phosphorus recirculation.

Management of the lake iron cycle requires manipulation of oxygen in the hypolimniom. Late in the summer or early fall before the lake cools and mixes, the hypo limnetic aerator is shutdown. The small amount of available oxygen in the sediment is quickly used up and oxidation environment quickly transforms to an anaerobic respiration process thus liberating ferrous iron into the water column. Phosphorus is also liberated at the same time. But the quantity of iron compared to phosphorous compounds is an order of magnitude higher – perhaps as much as 5 times or greater. During the fall lake turn over, oxygenated water from the surface which is higher in density, mixes down with the iron and phosphorus in aerobic exchange to precipitate (remove) the phosphorous. Each year, additional phosphorus enters the lake from the watershed (external loading). This P together with the recirculated P are both removed. As the lake begins a new growing season, the TP in the lake is indicative of any external loading not removed in the fall. This completes the iron cycle and has successfully reduced the internal TP loading in the lake by 90% and the total TP loading by about 30 -40%.

Nutrients of Phosphorus, Nitrates and Watershed Effects
The lake is surrounded by a watershed. The area of the watershed is mostly forested land. But in the early 1900’s, cottages and hotels were built along the shoreline on very small lots. Before electricity was available, water use was limited to spring water and lake water. Toilet use was by outhouses.

In the early 1930’s, JCP&L extended electric lines to the lake. People wanted running water so pumps were installed and pits were built to receive waste water. This was 30 years before NJDEP promulgated regulations on septic design. Fast forward to the present, approximately the same number of houses exist, some larger homes being built in the past 20 years, and some converted summer cottages converted to year round living. All homes in the lake community are served by septic systems and some of these systems have been in operation for decades.

The septic systems were placed at much higher density (approximately 4 homes/acre) then what would be permitted by zoning regulation today (1 home/5 acres). In the 1989 Culver Lake Study by Princeton Hydro (Coastal Engineering at that time), septic systems were identified as the number one cause of Culver Lake’s water quality problem.

A new approach to lake management as a result of this study set goals to restore the lake led to the installation of the aeration system and to reduce the internal nutrient load and implement a septic management plan. In addition, because the lake was eutrophic, there was an excess of alewife fish and a disparity of algae eating zooplankton. The study recommended stocking hybrid bass and aggressive seining of the alewives. The Normanoch adopted this lake management strategy and still adheres to these original recommendations today.

Septic systems within 100 meter distance to the shoreline are contributing the most nutrients to the lake according to scientific sources. There are two main components of nutrients that affect the water quality: phosphorus and nitrate. Both are products of human activity.

Since the lake is phosphorus limited, even small amounts entering the lake via ground water or surface water from the watershed causes increased growth of algae and lower clarity. Septic systems can discharge to the disposal field as much as 15 micrograms per liter of phosphorus depending on the number of house occupants and the amount of water that is consumed. The Normanoch has requested its members to have their septic tanks pumped at an interval of every three years for seasonal use and once every two years for year round use. Normanoch will reimburse $100 for pumping every two years.

Previously, fertilizer and detergents that did contain phosphorous no longer are available to the public. Chemical based fertilizer contains nitrogen and potassium and no phosphorus. Fertilizing lawns with the wrong product at the wrong time can result in nutrient water runoff to the lake. Maintaining a healthy lawn by not cutting the grass short will reduce evaporative losses, withstand dry periods longer than a lawn not properly cared for.

Phosphorus and nitrogen can come from other than septic systems sources. Leaves, clippings, dirt, run-off all contain these elements that are harmful to the lake. Phosphorus is known to attach to the dirt particles. Normanoch rules forbid discharging debris in the water such as leaves, clippings, compost and garbage.

The Normanoch Association and the Greater Culver lake Watershed Conservation Foundation both support watershed management of storm water on their properties so that rain water is absorbed in the soil rather than discharged over the ground where it picks up nutrients before entering the lake. Rain gardens are an excellent way to deal with runoff. A well designed rain garden can absorb a 1 inch storm event. Rain barrels, another method of managing storm water, can provide a source of garden water in dry weather.